Monday, April 27, 2015

I am in the market for a Keyboard controller with CV and gate outputs, but am having difficulty winning a cheap on e on ebay lately. This has led me to explore alternate options. I thought it may be reasonable to mod my existing keyboard considering it has MIDI output which can be converted into CV!

Sadly my Miracle Piano is the only keyboard I own right now, so it will have to do. It has a lot of space on the inside, but not all of it is located in the best of locations. Looking here, there is a 2" x 5.75" space perfect for adding pots or 3.5mm jacks.

I also have the prefect schematic to add inside. It is MFOS's MIDI2CV board:

This board requires +12v and -12v to power the op amps, but the rest of the board runs on +5v. I may or may not add a designated 5 volt regulator, or I may tap into the 5volts on the keyboard. Either way, I need to make sure I get a regulated +12volts so I will have to do some probing around to find a source. The keyboard requires 12VAC to run, but I have been running it on 9VAC...

Without looking at the power section on the board, I expect it to have either a transformer or a bridge rectifier. Hopefully I can access both positive and negative 12 volts. If I cannot I will have to limit the op amp outputs. I really don't want any clipping here...

I want the keyboard to work on the 1volt per octave scheme, but also be able to scale differently with knobs for gain and offset. This would allow for me to change octaves and such. Worse case scenario, I can add internal trimmers to permanently set the offset and gain to a fixed octave.

I also need to make sure the keyboard retains all of its existing functions, which it should. I also want it to fit comfortably without too heavy of modding. I may have to open this thing up several more times after installation. Maybe for more mods!

My design so far is smaller than 2"x5" but he connectors would not fit on the same board. The idea is to stack a second board with headers to connect all of the circuit to the I/O connectors. Then the I/O board will be fastened to the shell by the potentiometers and jacks.

I think that I will design this as a euro module first and foremost, but also keep the board within these few strict rules so I can transplant it into the keyboard. I like this idea the more I think about it.